How a Landlord Built a Pyramid-Shape Townhouse in His Own Backyard

A retired pharmaceutical executive fits a ‘ship in a bottle’ piece of architecture into a corner of his Berlin property

Ulrich Köstlin, a retired pharmaceuticals executive in Berlin with an eye for emerging art, wanted to create a compelling work of residential architecture. He found the chance in his own backyard—literally.

The courtyard, accessed through a multifamily rental he owns and where his son lives, offered just enough space—about 1/12th acre— for the planned two-family house. The challenge was to make the best of the small lot without crowding nearby apartment blocks. His architect likened it to “putting a ship in a bottle.”

The resulting structure is a creative, upscale, five-story townhouse. It is up against a neighboring apartment building’s firewall and a short walk across a paved open space from the multifamily building. It cost $3 million.

The project has caught the attention of architects beyond the city as an efficient way to build on such spaces. The property is located in the rapidly gentrifying Prenzlauer Berg district.

“I wanted to set an example of what architecture can contribute to city life,” Mr. Köstlin said.

Mr. Köstlin, 64 years old and a longtime Berlin resident, bought the property in the mid-1990s—not long after German reunification opened up East Berlin to investment from the West. It consisted of the front building and a newly vacant lot behind it. He paid about $470,000. Mr. Köstlin has spent the past 20 years doing piecemeal renovation of the building, which has 10 units and a ground-floor restaurant.

Luxury detailing sets the courtyard townhouse apart from its neighbors. In contrast to the plaster facades and bulky balconies nearby, the townhouse has a sculptural brick facade, with a streamlined pyramid shape at the top.

The aim of Mr. Köstlin, a former member of the executive board of Bayer, was to create a few large, luxury apartments in an up-and-coming neighborhood. He also wanted to minimize noise during the construction phase, then maximize views and light for neighbors after the building was finished.

The plan devised by his architects was to use a prefabricated concrete core to shorten construction time, and give it a shape that would make it less intrusive.

The design allows for an airy interior with large, bespoke windows with reflecting glass that gives privacy to residents. The windows cost $287,000.

The two lower floors of the new building comprise a 3,000-square-foot, three-bedroom, three-bathroom rental. On the three floors above, there is a 2,500-square-foot, three-bedroom, three-bathroom home, where Mr. Köstlin’s daughter, Berlin pediatrician Luisa Köstlin, lives with her 9-year-old son, Moritz. They will soon be joined by Dr. Köstlin’s fiancé, Ervin Beta. The doctor is expecting a second child in December.

Mr. Köstlin worked with the Berlin architecture office of Barkow Leibinger, known for the austere concrete space it designed for Berlin’s prominent Sprüth Magers gallery, which works with such artists as German photographer Andreas Gursky and American artist Cindy Sherman. Both the gallery and the townhouse include the studio’s signature use of smooth, concrete interior surfaces, such as the public stairway connecting the townhouse’s two units and the naked ceilings of the apartments.

The townhouse replaces a rear building that was once a partner to the six-story front building that faces the street. Damaged during World War II, it remained a ruin, says Mr. Köstlin, until the final years of the Communist regime, when two men and a wheelbarrow were sent to clear it way. “It took a year and a half,” he recalls residents telling him.

The new building took nearly as long to build, starting construction in January 2015 and finishing up in July 2016.

After buying the property, Mr. Köstlin tried to turn the yard into a communal garden for tenants in the front house, but found no one was willing to join in the upkeep.

The tight courtyard was a challenge. A crane parked on the street lifted materials over the top of the front house onto the construction site. Overall, Frank Barkow—Mr. Köstlin’s American-born, Berlin-based architect—estimates the inaccessible site added as much as $453,000 to the budget.

In his daughter’s unit, the top floor is a single, light filled, salon-like room, with enormous oak-lined windows. She says she and her son have gravitated toward the level beneath, with its open-plan kitchen and living room.

A local cabinetmaker created bespoke kitchens for the two units, at a total cost of $70,000. There are oak floors throughout.

Her apartment’s three bedrooms are on the unit’s lowest floor, which is the townhouse’s third level. But a growing family has made her wonder if her top-floor salon might be better used as a master bedroom.

“We would have to add a door,” she says, of the space. “But those stairs are very beautiful, and it might ruin the experience.”

Mr. Köstlin’s main luxury splurge was the townhouse’s distinctive brick exterior, comprised of five colors of bespoke masonry. It cost about $483,000. The colors, from pink to orange to gray, were inspired by the colors of the neighborhood apartment blocks. Many of these buildings date back at least a century and have been restored during years of gentrification.

The new building’s brick facade was made-to-order in a factory outside Berlin and required on-site construction of elaborate samples to perfect the subtle color scheme. The extra time and money “were worth it,” says Mr. Köstlin, who lives in his own restored townhouse in Berlin’s Mitte district.

“The brick layer is quite beautiful, and it has became a trademark for the building.”